What is your guidance regarding latecomers to prayer who do not begin their prayer until after the Imam has finished the rak'ah and begun a new one?

The Sunnah for someone who joins the prayer late (masbuq) is to join the Imam in whatever posture he finds him (bowing, prostrating, or sitting), based on the Prophet's (peace and blessings be upon him) saying: "When one of you comes to the prayer and the Imam is in a certain posture, let him do as the Imam does." This is what the people of knowledge (scholars) hold, even if that particular rak'ah does not count for him if he missed bowing with the Imam. This is supported by what Ahmad and Abu Dawud narrated from Mu'adh (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Mu'adh has set a sunnah for you, so do likewise," after Mu'adh joined the Prophet (peace and blessings be upon him) in prayer in the state he found him and then made up what he had missed. The masbuq joins the Imam with a valid takbir (Allahu Akbar), even if what he catches of the rak'ah does not count for him.